The present invention pertains to an insulation system for shafts through which hot gases flow, especially exhaust gas shafts of gas turbines with an insulation layer as well as a flat cover, which holds the insulation layer and covers it against the gas flow, wherein the cover is guided by bearing rails.
Such insulation systems are used in the diffusor and flue area of gas turbines. The insulation systems are exposed to gases with high temperatures above 400xc2x0 C. in these areas. In addition, there is a high velocity of flow above 30 m/sec in the diffusor area of the gas turbine. As a result, high thermal and dynamic stresses occur on the insulation system, especially on its holding systems, the cover, the bearing rails, fastening bars (spacers) for fastening the bearing rail on a wall of the shaft, etc.
The cover, the bearing rails and other fastening parts of the insulation system are usually made of a temperature-resistant metal with respect to the temperatures occurring. This also applies to the spacers, by which the bearing rails are fastened to the shaft wall. Thus, the spacers form heat bridges, through which the heat can be transported from the exhaust gas flow of the gas turbine into the shaft wall, because spacers made of metal are good heat conductors. It is therefore important to use as few spacers as possible. This goal is achieved, in principle, already by the use of bearing rails to which the cover for holding the insulation layer is fastened. The bearing rails have sufficient inherent stiffness to securely hold the cover. At the same time, the bearing rails and the cover must have a sufficient possibility of movement while still ensuring a secure hold in order to compensate even great temperature variations by thermal expansion and dynamic stresses.
In insulation systems of this type which are known from practice, this is guaranteed by the bearing rails being connected to the spacers with a certain clearance when viewed in the longitudinal direction of the bearing rails. Moreover, it is known that spacers can be made of a flat steel, in which case the flat steel is arranged in a plane extending transversely at right angles to the longitudinal axis of the bearing rails. Axial expansions in the bearing rail can thus be compensated by the bending of the flat steel. However, considerable stresses, especially bending stresses on the spacers, still continue to occur in these systems, so that a large number of spacers still continues to be necessary. In addition, the prior-art systems have the drawback that a considerable manufacturing effort is associated with them but the degree of prefabrication is low. The prior-art systems must be assembled almost exclusively at the construction site.
Based on this, the primary object of the present invention is to improve an insulation system of the type mentioned in the introduction such that the number of spacers by which the bearing rails are fastened to the shaft wall is minimized and they can be manufactured in the workshop with a high degree of prefabrication with low assembly effort at the construction site.
To accomplish this object, the insulation system according to the present invention is characterized in that the bearing rails are fastened to the shaft wall with a fixed mount and at least one movable mount.
The bearing rail is fixed by the insulation system according to the present invention in at least one point, while it is freely movable in its longitudinal direction in the other fastening points designed as movable mounts. Each bearing rail is thus mounted in a statically defined manner at each temperature and consequently at each amount of thermal expansion. Bending stresses acting on the spacers cannot occur, so that it is possible to work with a minimum of spacers. Depending on the length of the bearing rails, even one fixed mount and one movable mount are sufficient. These can be prefabricated almost completely in the workshop and then be assembled completely at the construction site.
It is particularly favorable for the bearing rail to be fastened to the shaft wall with an approximately central fixed mount and two outer movable mounts. The bearing rail is fixed approximately in the middle and can expand freely as a consequence of thermal expansion in both directions. It is, of course, also possible to provide a plurality of movable mounts on both sides in the case of longer bearing rails.
According to a variant of the present invention, the cover is connected to the bearing rails in a non-positive manner, especially by means of clamping strips. The cover is thus also able to expand freely during temperature variations without unacceptable thermal stresses building up. It is particularly favorable for the cover itself to be connected to the bearing rail in a positive-locking manner in the area of the fixed mounts of the bearing rails. According to one design embodiment of the present invention, this is accomplished by providing a notch in the bearing rail in the area of the fixed mount, which notch is engaged by a projection on the cover in a positive-locking manner.
Further features of the present invention pertain to design details of the movable mount and to the fastening of the cover to the bearing rails.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.